<p>One should be aware that there are a number of different DBM file formats
in existence, and with all likelihood, libraries for more than one format
may exist on your system. The three primary examples are SDBM, NDBM, the GNU
project's GDBM, and Berkeley DB 2. Unfortunately, all these libraries use
different file formats, and you must make sure that the file format used
by <var>filename</var> is the same format that <code>dbmmanage</code>
expects to see. <code>dbmmanage</code> currently has no way of determining
what type of DBM file it is looking at. If used against the wrong format,
will simply return nothing, or may create a different DBM file with a
different name, or at worst, it may corrupt the DBM file if you were
attempting to write to it.</p>
<p><code>dbmmanage</code> has a list of DBM format preferences, defined by
the <code>@AnyDBM::ISA</code> array near the beginning of the program. Since
we prefer the Berkeley DB 2 file format, the order in which
<code>dbmmanage</code> will look for system libraries is Berkeley DB 2,
then NDBM, then GDBM and then SDBM. The first library found will be the
library <code>dbmmanage</code> will attempt to use for all DBM file
transactions. This ordering is slightly different than the standard
<code>@AnyDBM::ISA</code> ordering in Perl, as well as the ordering used by
the simple <code>dbmopen()</code> call in Perl, so if you use any other
utilities to manage your DBM files, they must also follow this preference
ordering. Similar care must be taken if using programs in other languages,
like C, to access these files.</p>
<p>One can usually use the <code>file</code> program supplied with most
Unix systems to see what format a DBM file is in.</p>
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